Actor Patricia Clarkson was also present at the premiere. (Reuters)

Conventional wisdom holds that actresses fade into obscurity in their forties but, even at 62, Meryl Streep continues to astonish.

Re-teaming with her Mamma Mia!, director Phyllida Lloyd, the peerless performer portrays Margaret Thatcher in this biopic of the first, and only, woman prime minister of the UK. Her long overdue third Oscar was richly deserved.

The smartly structured script by Abi Morgan, the production's third notable female collaborator, moves back and forth in time through recent British history.

In the largely fictionalised opening segment we see the widowed baroness, now in her 80s, reluctantly clearing out the personal belongings of her late husband (Broadbent, terrific as usual).

Suffering from symptoms of dementia, she still 'sees' and converses with her spouse never mind that he died several years ago. Reveries of the past trigger flashbacks which chart her ascent to England's top political office.

Displaying indomitable will, Thatcher remained at the conflicted centre of late 20th century politics until her forced resignation in 1990.

The random recollections mostly steer clear of the controversial policies which led to her vilification. Prominent events such as the Northern Ireland strife, labour unrest and the Falklands conflict are also glossed over.

We never for a moment doubt Thatcher's ambition. She steamrolls the male establishment, which stands in the way of her, bid for 10 Downing Street. Eventually, the once all-powerful leader has to learn to live with her fears, infirmities and loneliness.

Monopolising almost every frame, Meryl Streep invests The Iron Lady with rare authority. In fact, the rest of the film pales in comparison.